The present invention relates to a multi-type air conditioner with an optimum control for each load and, more particularly, to a multi-type air conditioner with a heat pump-type refrigeration cycle for controlling a plurality of indoor units with a single outdoor unit.
A conventional air conditioner of this type controls the ON/OFF function of a capacity-fixed compressor provided within a single outdoor unit in accordance with temperature data from indoor temperature sensors respectively provided in a plurality of indoor units.
In this case, the plurality of indoor units are connected to the single outdoor unit through a distribution unit, so as to be parallel with each other. At the same time, the overall system constitutes a heat pump-type refrigeration cycle. More specifically, an outdoor unit, a liquid-side distribution unit, a plurality of indoor units, a gas-side distribution unit, and an accumulator are connected to a compressor in a looped manner through a 4-way valve. The outdoor unit comprises a capacity-fixed compressor, the 4-way valve for switching cooling/heating, an outdoor heat exchanger, a parallel combination of a cooling check valve and a heating expansion valve, and a liquid tank. The liquid-side distribution unit comprises a plurality of electromagnetic opening/closing valves. The indoor units comprise a cooling capillary tube and indoor heat exchanger, respectively. The gas-side distribution unit comprises a plurality of electromagnetic opening/closing valves. In the cooling mode, a refrigerant is flowed in the direction of the above connection order. In the heating mode, the refrigerant is flowed in the opposing direction to the connection order. A cooling/heating cycle is thus formed.
In the air conditioner described above, indoor temperature thermo circuits are respectively provided in the plurality of indoor units. For example, when the temperature of a room in which one indoor unit is installed reaches a set value and the indoor temperature thermo circuit of the loop is turned off, the liquid- and gas-side opening/closing valves of the loop are closed in order to stop flow of the refrigerant into the indoor heat exchanger of this indoor unit. When the indoor temperature thermo circuit is turned on by a change of the temperature caused by the operation interruption, the liquid- and gas-side opening/closing valves are opened in order to flow the refrigerant to the indoor heat exchanger. Note that a difference of 2 to 3 degrees is provided for turning on/off the indoor temperature thermo circuit.
When the conventional air conditioner is turned on/off, however, a variation in the room temperature is large, and comfort is thus degraded. In addition, when the compressor is turned off during cooling, the room temperature is increased, and the room may feel hot and humid. When the compressor is turned off during heating, the temperature of the air flow to the room is decreased, and a person in the room may feel cold.
In the other hand, a single type air conditioner for performing air conditioning by controlling a single indoor unit with a single outdoor unit, a variable control capability system has recently been adopted. More specifically, the air conditioner of this type variably controls the frequency of a compressor motor in accordance with the air-conditioning load state. With this air conditioner, the variation in the room temperature can be reduced compared to the case of the air conditioner of the ON/OFF control system, and the comfort can hence be improved. In addition, since the compressor motor is constantly driven, the non-effective power can be decreased compared to the case of the air conditioner of the ON/OFF control system. The energy-saving property is thus excellent.
When the variable control capability system is applied to a multi-type air conditioner, several problems must be solved, i.e., it must be studied in what manner the refrigeration cycle must be variably operated when a plurality of indoor units are controlled by a single outdoor unit. The problems include the conditions for variably driving the compressor motor and the arrangements of various types of valves. Another of the problems concerns the difference in the air-conditioning capability of the respective indoor units.
Conventionally, however, no effective answer has been given to these problems, and thus a multi-type air conditioner employing the variable capability control method has not been provided yet.
At present, since a multi-type air conditioner cannot but employ the ON/OFF control method, a variation in the room temperature is large, comfort is degraded, and the energy-saving property is also degraded.